1. Field of the Invention
The present invention relates to an image forming apparatus that performs image formation by an electrophotographic method, such as a copying machine, a printer, a facsimile apparatus, or a multifunction peripheral.
2. Description of the Related Art
In an electrophotographic image forming apparatus, a toner image is electrostatically transferred onto a transfer material by applying voltage having a polarity opposite to that of toner to a transfer member that is arranged so as to face a photosensitive drum and an intermediate transfer body serving as image bearing members. Then, the toner image is fixed onto the transfer material by heat and pressure at a fixing unit.
The transfer material is conveyed from a sheet supplying cassette to a transfer unit and a fixing unit sequentially by a conveying roller and a conveying belt and is adjusted to be conveyed properly by a conveyance guide and a sensor, which are arranged in a conveying path.
A conveyance member such as the conveying roller, the conveying belt, the conveyance guide, or the sensor is charged when making contact with the transfer material and easily discharges electricity to the transfer material or other members particularly under a low-humidity environment. When the discharging occurs, image defect for the transfer material and operation failure of the image forming apparatus due to noise are caused in some cases. Thus, a configuration is known in which the conveyance member is a conductive conveyance member and electrically grounded, and thus charges in the conductive conveyance member are released to the ground and charging of the conductive conveyance member is suppressed.
When the conductive conveyance member is grounded, however, particularly under a high-humidity environment, transfer current is likely to leak from a transfer unit to the conductive conveyance member through a surface direction of the transfer material. Thus, Japanese Patent Laid-Open No. 2001-139185 discloses a configuration in which a conveyance guide is grounded through a resistor to thereby suppress leakage of transfer current to a conductive conveyance member.
However, with the configuration for grounding through the conductive conveyance member as Japanese Patent Laid-Open No. 2001-139185, it is difficult to suppress overcharging of the conductive conveyance member when resistance of the resistor is excessively high and to suppress leakage of the transfer current to the conveyance member when the resistance of the resistor is excessively low. Therefore, it is difficult to simultaneously suppress the charging of the conveyance member and the leakage of the transfer current.